Search: id:A123751
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%I A123751
%S A123751 5,266681,40799043101,86364397717734821,
%T A123751 36190908596780862323291147613117849902036356128879432564211412588793094572280300268379995976006474252029,
%U A123751 3342798809452460123730317362957744184794205596648003071233209015009225097889080328310039011085108160910671510\
               27837158805812525361841612048446489305085140033
%N A123751 Primes in A007406[n].
%C A123751 A007406[n] are the Wolstenholme numbers: numerator of Sum 1/k^2, k = 
               1..n. Numbers n such that A007406[n] is prime are listed in A111354[n] 
               = {2,7,13,19,121,188,252,368,605,745,1085,1127,1406,...}.
%H A123751 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               HarmonicNumber.html">Harmonic Number</a>.
%H A123751 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               WolstenholmesTheorem.html">Wolstenholme's Theorem</a>.
%H A123751 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               WolstenholmeNumber.html">Wolstenholme Number</a>
%F A123751 a(n) = A007406[ A111354[n] ].
%e A123751 A007406[n] begins {1, 5, 49, 205, 5269, 5369, 266681, 1077749, 9778141, 
               ...}.
%e A123751 Thus a(1) = 5 because A007406[2] = 5 is prime but A007406[1] = 1 is not 
               prime.
%e A123751 a(2) = 266681 because A007406[7] = 266681 is prime but all A007406[k] 
               are composite for 2 < k < 7.
%t A123751 Do[f=Numerator[Sum[1/i^2,{i,1,n}]]; If[PrimeQ[f],Print[{n,f}]],{n,1,250}]
%Y A123751 Cf. A111354, A007406, A001008, A007407, A067567, A056903.
%Y A123751 Sequence in context: A151589 A038027 A057679 this_sequence A152516 A067502 
               A067509
%Y A123751 Adjacent sequences: A123748 A123749 A123750 this_sequence A123752 A123753 
               A123754
%K A123751 nonn
%O A123751 1,1
%A A123751 Alexander Adamchuk (alex(AT)kolmogorov.com), Oct 11 2006

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